Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. As a result, over the years, well architecture has become more sophisticated where appropriate in order to help enhance access to underground hydrocarbon reserves. For example, as opposed to land based oilfields accommodating wells of limited depth, it is not uncommon to find offshore oilfields with wells exceeding tens of thousands of feet in depth. Furthermore, today's hydrocarbon wells often include a host of lateral legs and fractures which stem from the main wellbore of the well toward a hydrocarbon reservoir in the formation.
In addition to the complexities of the field itself, the oilfield business itself may also be quite complex. For example, it is not uncommon for a variety of different wells at a given field to have multiple owners. This might include the circumstance where a single well is owned by multiple producers. Similarly, circumstances may involve several wells at an oilfield that are separately owned but which are produced to a single location and/or serviced by a single manifold such that the production from different wells is combined.
Multiple producer ownership allows owners to share the expenses and risk of operations. However, the arrangement introduces accounting issues. For example, where ownership is different from one producing well to the next, there is a need to couple a flowmeter to each well at some location before the production fluids are combined and produced to surface.
Conventionally, it makes sense to place a flowmeter assembly directly at the well, for example, by incorporating the flowmeter into standard Christmas tree hardware at the wellhead. The assembly may be added to the Christmas tree at surface before installation of the tree. However, for a cluster of wells, this requires that each Christmas tree of the cluster be outfitted with a substantial amount of added hardware. That is, in addition to the flowmeter itself, a sizeable landing structure is also required to accommodate the flowmeter. This usually translates into upwards of four cubic feet of volume and perhaps up to 1,000 lbs. or more being added to each tree. Thus, not only is the installation more challenging and time consuming but it is also much more costly.
In an effort to reduce costs, flowmeter assemblies may be added to a manifold that services the same cluster of wells. In this way, the trees may be installed without concern over the added costs and challenges associated with supporting individual flowmeter assemblies. Instead, this issue is transferred over to a manifold. As a practical example, this means that rather than performing six different installations with flowmeter assembly challenges, a single manifold with six different dedicated flowmeter assemblies may be installed a single time.
Unfortunately, while transferring the challenge from six trees to a single manifold may add some efficiencies, it does not actually remove the challenge altogether. Indeed, in certain respects, the challenge grows. Continuing with the example above, the challenge literally grows in terms of the sheer size increase of the manifold. Already a several thousand pound piece of equipment, the new manifold with integrated flowmeters has likely grown thousands more pounds and increased in size by 30-50%. This is because six different flowmeter assemblies, each about 4 cubic feet in size, have been added to the connection points on the manifold, one for fluid pairing to each well and tree.
If operators are able to install such a manifold, it will save time spent on installation of the Christmas trees at the wellheads. However, the challenge of such a massive installation can be daunting. For example, the sheer size of the manifold may mean that only one manifold may be installed at a time at an oilfield due to the limitations on the capacity of available installation vessels. Once more, the installation time may also be increased. Ultimately, these factors may mean that days may be added to the complete installation time. This not only costs in terms of lost time, but it also means that installation vessel expenses, generally over $250,000 in today's dollars are driven up.
As indicated, some efficiencies may be achieved through incorporating flowmeter assemblies on manifolds. However, as a practical matter, operators often opt to incorporate these assemblies on Christmas trees due to convention and to avoid the risks and challenges associated with incorporating flowmeter assemblies on manifolds.